Conventional roller shutters are designed to provide security from break-ins and protection from storms. Because such protection and security may not always be necessary or desired, such as during the day when a retail store is open for business or during fine weather when a homeowner wishes to open windows, roller shutters are designed to be retractable into a casing in which they are stored. To facilitate compact storage, the rigid shutter slats that are designed to resist hurricane winds and burglars must be capable of conforming to a roll.
The slats of roller shutters are commonly aligned and held in place by guides, or side tracks. End retention systems are known for use in rolling shutters and doors to keep the shutter curtain engaged in the side tracks during pressure caused by winds, or by would-be intruders attempting to force the shutters open. Several types of end retention systems are known in the art. Some of these systems change the diameter of the roll at the spot where the end retention system has been placed. Special tracks have been designed to provide special channels for end retention systems so that the end retention system does not change the rolled curtain configuration at these points where the end retention system is installed.
These special tracks may be undesirable because they may require special channels that limit the amount of horizontal travel, or “slip” (travel in the plane of the shutter that is perpendicular the direction of opening and closing of the shutter, which is usually vertical) the shutter curtain has in its operation. This limited amount of slip increases the pressure on the fastening system that holds the guides to the structure caused by catenary forces established when the curtain is put under load. It may be desirable to increase the amount of slip that the shutter curtain can absorb before the load is transferred to the fasteners due to the retention of the shutter slats.
Another drawback of the channels of these special tracks is that they may increase the necessary sophistication of the overall shutter design to allow for funneling the end retention system into the channels and for keeping the shutter curtain correctly aligned. Typically, the end retention system has an end that is no wider than the width of the profile of the slats of the shutter, so that there is no change in the rolled configuration. To accommodate this, the diameter of the end retention system may be reduced to allow for the system to move in the void between the end retention fins of the side tracks.
One simple end retention system of this type is a screw that fastens into the shutter curtain profile, for example to the side of a slat, and extends beyond the end retention fins of the side track. The screw may have a large head that is roughly equal to the width of the curtain profile (which is generally the same as the width of the profile of a single slat) so it is not so large as to increase the diameter of the rolled curtain, but large enough that it will be held captive by the end retention fins of the side track.
One problem that may arise with this type of end retention system is that a moment may be created in the screw (fastener), because it extends from the curtain profile and may act as a lever. If the end retention system happens to be out of line or catches on the retention fins of the side tracks or something else, the system can be bent or torn out and can cause a malfunction of the operation of the shutter curtain. To increase the desired slip in a system using special tracks, the channel sizes may need to be increased, which requires more material, and may also increases the possibility of failure due to increased moment of the longer shaft.
It may be desirable to maximize the engagement between the end retention fins and the end retention system. Many known end retention systems limit the end retention system's size to be no wider than the curtain profile depth, so that the retention system does not engage an adjacent profile or an adjacent profile's end retention system when the shutter curtain is rolled up. These types of end retention systems, however, may limit the amount of engagement between the end retention fins and the end retention system.
If the desirable level of engagement is attained, it may be possible to reduce the number of end retention systems used in a shutter curtain. Instead of using an end retention system in every slat, for example, it may be possible to only install an end retention system in every other slat, every third slat, or the like, and still achieve a desired strength. Systems that attain this increased engagement are referred to herein as “increased engagement end retention systems.”
One known increased engagement end retention system is the Alulux CD41/S end retention system, which is configured to be inserted into the hollow profiles of a number of slats in a shutter curtain. This end retention system has a shape such that if one system interferes with an adjacent system when the shutter curtain is rolled up, the system will slide off of the adjacent system, realigning the curtain. This resulting movement of the shutter slats can put undue force on these systems, and may be undesirable because it could loosen or dislodge the end retention system. One could calculate which end retention system is likely to engage another in a given shutter design, and could extend some systems so they do not engage adjacent ones. This extension may be undesirable, however, because it difficult to insure the correct systems are extended, and because the systems may not all engage the retention fins uniformly when the shutter is put under a load. Such a system also may not be a good solution for single wall shutter profiles, because of the limited shutter curtain profile width and lack of interior cavity make affixing such an end retention system difficult.
Another increased engagement end retention system is the ALULUX CD 77/2 system, which slips out of the way of an adjacent system when the shutter curtain is rolled up. This system only lets the end retention system slide in one plane. This system uses multiple points of engagement or tracks to maintain the movement on this desired plane.
This ALULUX CD 77/2 increased engagement end retention system has an increased engagement because the system is wider than the width of the curtain profile. This end retention system can be used with a less complex side track system; such as such as the ALULUX UP 250/S, to retain the shutter profile in the side track. This arrangement may allow for an increase in the desired slip without changing the shape of the side tracks, since the end retention system is wider than the width of the curtain profile when in the side tracks. Also because this end retainer system is adjacent to the curtain profile it significantly reduces the moment put on the attachment system to the curtain profile making it stronger and less prone to failure. However, this end retention system achieves these benefits by its increased size, and therefore suffers from the problems described above regarding large end retention systems.
Generally, the use of end retention systems may allow for the use of smaller and thinner curtain profiles to attain desirable resistances to pullout. These smaller and thinner curtain profiles are desirable because they require less material to manufacture, they are able to roll up in a smaller diameter requiring less material to house the rolled shutter, and they reduce the torque required to operate the shutter due to the decreased overall weight of the shutter curtain. However, increased engagement end retention systems generally are not easily adaptable for use with these thinner profile shutter curtains. It would be desirable to provide an increased engagement end retention system that is adapted for use with thinner (single walled) shutter curtains.